of certain inflammable gaseous compounds. 13 
considered as consisting of 1 proportional of carbon = 5,7 -J- 
2 proportionals of hydrogen = 2, and its specific gravity has 
been stated as 7,7 compared with hydrogen ; or as 57365, 
assuming atmospheric air as 1. 
My first object in the examination of coal gas was to as- 
certain its specific gravity ; and I was surprised to find the 
first that I examined so low as ,44,30. There was some varia- 
tion in different specimens ; and the specific gravity of that 
prepared in the laboratory of the Royal Institution, and puri- 
fied in the usual way by condensation in cold vessels, and 
passing through lime water, was as high as ,4940, which is 
the heaviest that I have yet met with. 
Having been led to consider coal gas as consisting essenti- 
ally of the two varieties of carburetted hydrogen, I imagined 
that the specific gravity of the light hydrocarburet must have 
been estimated too high ; I therefore prepared light hydro- 
carburet from acetate of potash, and having separated its 
carbonic acid by lime, found its specific gravity ,687 ; the 
specific gravity of the gas from stagnant water, according to 
Mr. Dalton,* is ,600, and that from moistened charcoal 
when purified is ,48o. , f It became evident, therefore, that 
coal gas could not consist principally of the two hydrocar- 
burets ; nor could the presence of carbonic oxide be suspected, 
its specific gravity being ,9834. Hence it occurred to me, that 
the only mode of explaining these apparent anomalies, was 
to consider coal gas as a mixture of olefiant and hydrogen 
gases ; and the following experiments were undertaken with 
a view to determine this point. 
* New System of Chemical Philosophy. f Henry’s Elements, p. 320. 
